PWM Pulse Help

[bearsomg]

I'm trying to design a computer program that will use the digital outputs of a computer's parallel port to control a jaguar through PWM. From what I know already, one pin goes to ground, but what are the other two pins on the PWM cable used for?

Also, how would I calculate the pulse on/off time to sending high/low values through the PWM pulse pin to set the Jaguar to certain speeds (I.e. what would I need to send through the 3 pins to get the equivalent of half speed on the jaguar output)?